Methods and devices for central photoplethysmographic monitoring methods

ABSTRACT

Disclosed herein are methods and devices for delivering gas to a subject and obtaining plethysmograph readings from a subject. Specifically disclosed herein are masks and helmets which comprise one or more pulse oximeter probes associated therewith. The masks and helmets may be used in particular contexts, including, but not limited to, emergency responder personnel, pilots or subjects of medical attention.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of International ApplicationNo. PCT/US05/28355 filed Aug. 10, 2005, whose teachings are incorporatedby reference, and which claims priority to U.S. Provisional ApplicationNo. 60/600,548, filed Aug. 11, 2004.

BACKGROUND OF THE INVENTION

Gravity-induced loss of consciousness (“GLOC”) is a prototypical exampleof a phenomenon of reduced cerebral blood flow that occurs when someoneis subjected to substantially increased gravitational loads (+Gz) for asustained period. High-performance aircraft, such as fighters, allowmaneuvers that generate +Gz that exceed the limits of the human body.This predisposes to GLOC and a serious degrading of physiological andcognitive performance. GLOC is one of the primary physiological threatsto pilots and crews of high-performance aircraft. Since the mid 1980s,one branch of the US military, the United States Air Force, has lost 29aircraft and 22 pilots to GLOC. (The Effect of Negative Gz Recovery fromGLOC on Cerebral Oximetry, Broughton, presentation at USAF School ofAerospace Medicine, Brooks AFB, Texas (2003).) Similar loss rates can beexpected for the other services flying high performance aircraft. Inaddition to the loss of life, the cost of training and lost aircraft isstaggering.

Almost loss of consciousness (ALOC) is even more common than GLOC.Symptoms include euphoria, apathy, displacement, depersonalization, poorresponse to auditory stimuli, immediate memory difficulties, sensoryabnormalities, motor abnormalities, confusion, and dream-like statewithout loss of consciousness, which are considered precursors of GLOC,which is defined as “A state of altered perception wherein one'sawareness of reality is absent as a result of sudden, critical reductionof critical blood circulation caused by increased G forces”.(Morrissette K L, McGowan D G. Further support for the concept of aG-LOC syndrome: a survey of military high-performance aviators. AviatSpace Environ Med. 2000; 71:496-500.; Burton RR, G-Induced Loss ofConsciousness: Definition, History, Current Status. Aviat Space EnvironMed. 1988; 59:2-5.)

Some methods have been developed to increase G-level tolerances,including centrifuge training, weight training, the anti-G suit,positive pressure breathing, anti-G straining maneuvers and posturalmodification in the cockpit. The current capabilities of trainedindividuals to maintain clear vision during sustained exposures to +9Gz, an increase in protected +Gz tolerance of about +4 Gz over World WarII fighter pilots, is largely a result of combined use of a G suit andself-protective straining maneuvers such as the M-1, L-1 and pressurebreathing, all of which are variants of the Valsalva maneuver developedin the 1940s. (G-induced Loss of Consciousness and its Prevention, EarlWood, (1988) Mayo Clinic, Rochestor, Minn.) However, despite suchtraining, a review of ten fatal crashes attributed to GLOC shows thatsuch measures fall short of addressing the problem. Id. The Wood reviewnotes that the likely causes of such failures were: (1) increasedcapability of jet-powered fighters to sustain, with minimal piloteffort, accelerations in the 7-10+Gz range for periods longer than thesymptom-free 3-8 second cerebral ischemic anoxic period which precedesGLOC, (2) an improperly performed Valsalva-type straining maneuver, and(3) development of a hypotensive vasovagal type reaction.

The inventors believe that currently used techniques do not adequatelyaddress the detection of reduced cerebral blood flow. For example, theproblem of GLOC (which for the purposes of this document pertains toboth ALOC and GLOC) puts the burden on the pilot to realize when he/sheis about to sustain GLOC. Further, reduced cerebral blood flow is aserious medical condition which can lead to irreversible brain injury.At present there are no simple and reliable technologies for measuringcerebral blood flow noninvasively. For example, decreased cerebralperfusion may occur during surgery, trauma, sleep disorders, cerebralvascular insufficiency (eg. Ischemic stroke), hypotension from a widevariety of causes or during ventilatory management

SUMMARY OF THE INVENTION

The subject invention pertains to methods, devices and systems ofobtaining plethysmograph readings and utilizing plethysomography toidentify reduced cerebral blood flow both when pilots are about toexperience GLOC and for training pilots to recognize signs and symptomsof impending GLOC. And in the medical environment where it can serve asan early warning system of impending cerebral ischemia and as a monitorto determine the presence and degree of cerebral flow. Clinicians can bewarned that the cerebral blood flow is decreasing and/or the system canbe integrated into closed loop system to optimize therapies that canimprove flow to the brain (such as ventilator management techniques,fluid resuscitation or drug delivery systems). Furthermore, in otherembodiments, the invention pertains to methods and devices designed towarn a pilot that he/she is about to sustain GLOC and/or automaticallyaverting catastrophic damage or injuries by directing the plane to takepredetermined corrective actions. In addition to airflight applications,the methods and devices herein can be used to monitor workers whose jobsrequire high stress situations or harsh environments, such as emergencyresponse teams. Finally, the subject invention allows measurements madeduring training in centrifuges and aircraft to be displayed forreal-time feedback to teach the pilot to optimize GLOC preventionmaneuvers and to be stored and used to provide an individual pilot'splethysmographic data for developing GLOC “profiles” which can beprogrammed into flight systems to determine when an individual pilot isentering the early stages of GLOC based on previously collected data.

According to other aspects, the subject invention pertains to novelpulse oximeter probes. The term “pulse oximeter probe” as used hereinrefers to probes that can be used for pulse oximetry determination ofarterial blood oxygen saturation and/or used for plethysmography.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a pulse oximeter/plethysmographyprobe designed for securement in the nose of the user.

FIG. 2 shows a side cross-sectional view of the embodiment shown in FIG.1.

FIG. 3 shows a side view of a user having a pulse oximeter probe asshown in FIG. 1 inserted and secured in their nose.

FIG. 4 shows mask and helmet embodiments having a probe associatedtherewith. FIG. 4A shows a side view of a pilot wearing a mask with aprobe. FIG. 4B shows a ventilation mask suitable for association of aprobe. FIG. 4C shows a nasal mask. FIG. 4D shows a mask for emergencyresponders and helmet. FIG. 4E shows a helmet suitable for associationwith a probe.

FIG. 5 is a schematic of an embodiment of the subject invention thatcomprises an analyzer unit integrated with an aircraft computer.

FIG. 6 is a diagram showing a schematic of an embodiment of the subjectinvention comprising an analyzer unit operationally coupled to anaircraft computer.

FIG. 7 shows a perspective view of a pre-auricular reflectance probeembodiment of the subject invention.

FIG. 8 shows a side view of a pre-auricular reflectance probe embodimentof the subject invention.

FIG. 9 shows a perspective view of an alar pulse oximeter probeembodiment.

FIG. 10 shows a front perspective view of the alar pulse oximeter probeembodiment shown in FIG. 9.

FIG. 11 shows a rear perspective view of the alar pulse oximeter probeembodiment shown in FIG. 9.

FIG. 12 shows a bottom view of the alar pulse oximeter probe embodimentshown in FIG. 9.

FIG. 13 shows a plethysmograph obtained from the right and left cheek ofan individual. FIG. 13 a shows the right and left plethysmograph withoutdepressing the carotid artery. FIG. 13 b shows the right and leftplethysmograph with pressing the right carotid artery. FIG. 13 c showsthe right and left plethysmograph after releasing the right carotidartery.

FIG. 14 represents a plethysmograph from a pulse oximeter probepositioned on the cheek. The AC component (or cardiac component forpurposes of this example) is provided on the top and the DC offset (ornon-cardiac component for purposes of this example) is provided on thebottom. Pressing on the carotid diminishes blood flow, as seen in the ACcomponent (see arrow). Conversely, the DC offset goes up when thecarotid is depressed (see arrows).

FIG. 15 represents a plethysmograph obtained from the finger. The DCoffset is plotted at the top and the AC component at the bottom.

FIG. 16 represents a diagram illustrating a method embodiment of thesubject invention for obtaining a personalized data profile for anindividual with information for determining whether individual is aboutto enter GLOC.

FIG. 17 represents a perspective view of a post-auricular probeembodiment.

FIG. 18 represents a perspective view of an ear canal probe embodimentfor obtaining plethysmography readings from a user's ear canal.

FIG. 19 represents a remote monitoring station to monitor one or moresubjects.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS OF THE INVENTION

Turning to FIG. 1, a nasal pulse oximeter probe 10 is shown designed forthe comfortable placement in the nostrils of a human or non-human. Thenasal probe 10 may be made of a wide array of materials, including, butnot limited to, silicon, rubber, plastic or other polymer-basedmaterials, or other suitable materials. Preferably, the nasal probe iscomprised, at least in part, of materials (similar to hearing aid earmolds) that are soft and flexible as to allow proper comfort by theuser, but possess enough rigidity to properly conform to the inner wallsof the nose and provide frictional resistance to secure the probe in theuser's nose. The nasal probe 10 comprises a first insert 16 havingdefined therein a channel 15 and a second insert 18 having definedtherein a channel 17. Channels 15 and 17 are of a dimension to allow forthe free-flowing passage of air as the user inhales and exhales in andout of the user's nose. Positioned in or on the medial wall of insert 16is a light generating source, such as a light emitting diode (LED). Aphotodetector 14 is positioned on or in the medial region of insert 18.Wires 20 and 22 are connected to the light generating source 12 inphotodetector 14, respectively. To assist in the management of wires 20and 22, wires 20 and 22 may be secured together by fastener 24, such asa sleeve. Those skilled in the art will appreciate than any means forholding together wires may be used for this purpose, including, but notlimited to, a clip, tie, ring, band, etc. Additionally, positioning thephotodetector and LED on the same wall of the same insert such that thesensor functions in a reflectance mode is also contemplated. A nasalprobe with a single insert (reflectance on either the alar wall on nasalseptal wall) is contemplated as well. Additionally a nasalinsert—transmissive with a flap/clip portion on the exterior of the nareis contemplated as well. Since reflective pulse-oximetry requires lightto return to approximately the same location as it was transmitted, avariety of reflective surfaces could be envisioned in this scenario aswell. For example, the transmitter and receiver could be co-located onone wall of the insert and the second insert could be made of aphoto-reflective material or contain a reflective surface. It is alsoenvisioned that the reflective material could be made to focus (like alens) scattered light back at the photodetector to: a) increase signalto noise ratio, b) help reduce motion artifacts, or c) reduce the LEDpower requirements (thus allowing longer battery operating times). Thissame technique could be used in various other orientations such as theLED and photodiode on the external side of the nare of the nose and asimple reflective material on the inside of the nose (or vice versa).This technique could allow more comfortable and less obtrusive materialsto be used in certain key locations. Further, if sensors are to be worncontinuously, especially in an ambulatory environment, less conspicuoussensors would improve acceptance and compliance with wearing thedevices.

In addition, the inventors do not intend to be limited to the type ofprobe that may be used. U.S. application Ser. Nos. 10/176,310;10/751,308; and 10/749,471 disclose various probe embodiments that maybe implemented for use in accord with the teachings herein. Theseapplications also teach the functional and technical aspects of the LEDand photodetector.

As used herein, the term “central source site” refers to a site above auser's neck, wherein information regarding blood flow at such sitecorrelates with blood flow to the user's brain. Examples of centralsource sites, include, but are not limited to, the tongue, lip, cheek,nasal nares, nasal septum, nasal alar, pre-auricular region,post-auricular region and ears.

FIG. 2 shows a cross-sectional side view of the nasal probe embodiment10 shown in FIG. 1. The LED(s) 12 and photodetector 14 are positionedacross from each other. To monitor oxygen saturation, two or more LEDsare typically required. For plethysmography, only one IR LED is needed.However, multiple LEDs are contemplated as well for increasedreliability, or for reliable measurement of dyshemoglobin, carbonmonoxide, other inhaled pollutants, or blood analytes such as glucoseand electrolytes. In addition, various types of CO2 sensors could beincorporated in the nasal probe. These sensors could include infraredspectroscopy, raman spectroscopy, colorimetry, and variousnanotechnology sensors. The CO2 sensor provides important ventilationinformation that could be used in hazardous material scenarios,ventilatory support, or sleep disorders. Further, without being limitedto any specific mechanism or theory, it is the belief of the inventorsthat the plethysmogram will show signs of reduced blood flow to the headsuch as GLOC far earlier than changes in oxygen saturation. However, itis contemplated that the probes and methods of the subject invention maybe designed and used to monitor both plethysmography and oxygensaturation of the user.

Insert 16 comprises a medial region 21 and a lateral region 25. Insert18 also comprises a medial region 23 and a lateral region 27. The user'snasal septum would lie in the space defined by the medial regions 21, 23of inserts 16, 18, respectively. Accordingly, the medial regionrepresents that portion of the insert that contacts the user's nasalseptum. The lateral region represents that portion of the insert that isproximate to the user's nares. Though the disclosed embodiment showsthat the inserts completely define an inner channel, with the inserthaving a medial region and a lateral region, the insert may be fashionedto define less than the full circumference around an inner channel.Wires 20 and 22 are connected to the LED 12 and the photodetector 14,respectively.

FIG. 3 shows a side view of a person having the nasal probe embodiment10 placed in their nostrils. Wires 20 and 22 are covered and fastenedtogether by a sleeve, which together form wire 32.

FIG. 4A shows a pilot 44 wearing a helmet 46 attached to a mask 40. Themask 40 comprises an air hose 48 attached to the mask compartment 43.The pilot has positioned in his nose 45 the nasal probe 10 shown inFIG. 1. Wire 32 containing wires 20 and 22 passes through hole 42defined in the mask compartment 43. It will be appreciated by thoseskilled in the art that the wire may be secured a number of differentways in the mask and/or air hose 48. For example, the hose 48 may have achannel defined therein through which the wire 32 may pass. Theembodiment shown in FIG. 4A would most likely comprise fastening thewire 32 to the outside of the hose 48 so that it does not obstruct theactions of the pilot 44. The wire 32 carries the signals from thephotodetector to a signal processor and analyzer unit to be discussed infurther detail herein. It is important to reiterate that the probe usedin conjunction with the mask, nasal, cheek or otherwise, is not limitedto the embodiment specifically shown. The mask 410 shown in FIG. 4B is atypical mask designed for non-invasive ventilation and the mask 412shown FIG. 4C is a nasal only mask commonly used for sleep disordersand/or used for therapies such as oxygen and noninvasive positivepressure ventilation therapies. These masks may be modified toincorporate a probe for obtaining photoplethysmography readings from acentral source site (such as the nasal alar or nasal septum similar tothat described and shown in FIG. 1). Mask 410 comprises a compartmentportion 421 configured for covering the nose and mouth comprising acompartment that defines a space into which gas is disposed. Thecompartment portion 421 is held to the face by strap 411. A probe 419,with alternative CO2 sensor attached or integrated (429), is shownpresent in the compartment portion 421 which may take the form of any ofthe probe designs discussed herein. Note that CO2 sensor may be separatefrom probe 419 but nonetheless associated with mask 410. Wiring 418 fromthe probe 419 associated with the mask 410 may be used to attach a smallbattery pack 420 for extended monitoring life and/or to attach awireless transmitter 422 for remote monitoring of the users status. Suchfeatures may also be implemented with other masks and/or helmets. Mask412 comprises a nasal gas delivery portion 423 which is configured withtwo nasal projections 425 configured for delivering gas to the nasalpassages. The mask 412 is held to the face with strap 413.

In addition, masks for protection from hazardous vapors or smoke (e.g.emergency care providers, firemen, or other hazardous environments,scuba, etc.) can also be modified to incorporate a probe for obtainingphotoplethysmography readings. In many of these situations, it isenvisioned that the masks could be wirelessly connected to a control orcentral location for continuous monitoring of the health and wellbeingof the emergency provider, pilot, or hazardous material crew. In oneembodiment the probe, could be built into an emergency responder'shelmet 414 or mask 416 such as that shown in FIG. 4D and/or 4E. Thehelmet 414 comprises a head cover portion 430, preferably, though notnecessarily, made of a rigid material to protect the head from fallingdebris. Integrated with the head cover portion 430 could be a tailportion 432 designed to extend protection to the neck and upper back. Aprobe (not shown) designed for obtaining photoplethysmography readingsfrom a central source site is associated with the helmet 414 and mask416, optionally with cabling (not shown) to a battery pack and/orwireless transmitter. The term ‘associated’ or ‘associating’ as usedherein means that the probe is attached, tethered such as via a cable,or integrated such as being embedded, to one or more parts of the helmetor mask. Also contemplated herein are probe embodiments comprising awireless transmitter and battery supply as one encased unit therebyalleviating the need for wiring to separate components. The helmet isalso secured to the head via strap 415. Typically, a protective padportion 435 lies between the strap 415 and the user. The mask 416 mayalso comprise a strap like that shown in FIG. 1 which holds the mask 416to the user's face. A preauricular or postauricular probe could beassociated with such strap or protective pad portion 435.

In an alternative embodiment, a pre-auricular probe (or post-auricularprobe) could be associated into a mask system as well. In thisembodiment, as shown in FIG. 4C, a probe 427 is attached to the strap413 The straps can provide an advantageous means for associating thecabling as well as for securing the probe in the proper position. It iscontemplated that an auricular probe may be implemented into straps 411or 415 as well.

Furthermore, the mask and/or helmet embodiments may include a CO2 sensorthat is associated with the mask or helmet. The CO2 sensor may be a partof the pulse oximeter probe or as a separate sensor. Alternatively, asampling apparatus to obtain exhaled gases for determination of carbondioxide content, may be associated with the mask and/or helmet. SeePCT/US2004/043610.

It is contemplated that one or more subjects may need to be monitoredremotely. For example, it is contemplated that a team of firemen workingin a dangerous environment may be monitored to increase their safety. Insuch example, the masks worn by the firemen comprise wirelesstransmitters that are communicatingly connected to a remote computer.The remote computer has processing module(s) and program code module(s)enabling the analysis of signals from the probe to evaluate blood flowand/or respiration so as to warn a user of when a fireman is approachinga dangerous physiological condition. A similar system may be implementedfor remotely monitoring one or more subjects in other contexts as well,including a military environment or a hospital environment with a nursestation to remotely monitor patients. A basic system embodiment is shownin FIG. 19. In this embodiment, a remote monitoring computer 1910 iscommunicatingly connected to a plurality of probes 1912. A user at theremote station is able to monitor signals of blood flow, respiration,CO2, and/or oxygen saturation of one or more subjects. This increasesthe safety of the subjects as the remote station can provide an earlywarning for when the subject is experiencing dangerous physiologicalcircumstances.

Turning to FIG. 5, there is shown a system 50 for processing signalsobtained from a pulse oximeter probe being worn by a pilot andconducting a reaction responsive to certain information received fromsaid pulse oximeter probe. The system comprises an analyzer unit 58 thatis configured to receive and process signals from lines 52 and 54. Thoseskilled in art will appreciate that the signals may be preprocessed tosome degree by a separate signal processor and subsequently sent as onesignal stream to said analyzer unit 58. Thus, the analyzer unit 58 isconfigured to receive signals from either lines 52 or 54 or acombination of both. The analyzer unit 58 comprises a processing module56 comprising software and/or electrical/circuitry components todetermine whether the signals received from the pulse oximeter probecorrelate to a loss in blood volume indicative of inducing GLOC. Theanalyzer unit 58 may also comprise a second processing module configuredto generate a warning signal.

During a typical high +Gz maneuver, a pilot is trained to take in amaximal deep breath as quickly as possible and to either hold it for ashort period of time while bearing down and then performing a rapidforced exhalation, or alternatively, to take in a deep breath and forcethe air out continuously against pursed lips. With either maneuver, theidea is to “trap” oxygenated blood in the head temporarily (3-5 seconds)and then rapidly allow the blood to return to the lungs. These maneuversare repeated at 5-10 second intervals throughout the high +Gz period. Itis both important to take in a maximal inspiration and then also to beardown and release the breath against resistance. Taking in a deep breathand bearing down forces blood to the head, but if the maneuver is heldfor too long, venous return to the heart is impeded, flow to the braindecreases and GLOC ensues. Thus, maneuvers to prevent GLOC are a “doubleedged sword” and must be performed correctly or they can actuallyexacerbate GLOC.

The disclosed system can be used during centrifuge and aircraft trainingto provide real time feedback via visual and/or auditory cues to helpthe pilot optimize these maneuvers. Additionally, when optimal maneuversare obtained, the system can store the plethysmogram that signals theonset of GLOC. This may be a system that evaluates the amplitude of thepre-+Gz plethysmogram and then recognizes when the plethysmographysignals have decreased by a predetermined percentage of the pre-+Gzvalue which is individualized for each pilot and determines when GLOC isimpending (as defined herein a pre-GLOC condition). Numerous factorsincluding the physical characteristics of the pilot influence theirability to withstand sustained +Gz loads. The individualized informationcan be loaded into a computer system that continually evaluates theplethysmogram (and therefore blood flow to the head) both during levelflight and during +Gz maneuvers and based on predetermined data candetermine that the pilot is about to experience forces and declines inblood flow to the head which will result in GLOC if the high +Gz load ismaintained. Previous research indicates that unconsciousness ensuesapproximately 5-8 seconds after cerebral blood flow (CBF) decreases by72-80% from baseline flow. (Florence G, Bonnier R, Riondet L, Plagnes D,Lagarde D, Van Beers P, Serra A, Etienne X, Tran D. Cerebral corticalblood flow during loss of consciousness induced by gravitational stressin rhesus monkeys. Neurosci Lett. 2001; 305:99-102.)

The GLOC warning system could be designed to evaluate the amplitude ofthe plethysmograph just as +Gz acceleration begins and monitor theamplitude of the plethysmograph during the +Gz maneuver. At a presetpercentage of the pre +Gz amplitude an alarm can be actuated. If thepilot does not respond to the alarm and the amplitude continues to droptowards the critical decrease in CBF (e.g., 65-85% below baseline flow)the autopilot could take control and decrease the +Gz load until theplethysmograph amplitude increases above a critical level.

Thus, according to another embodiment, as shown in FIG. 16, the subjectinvention pertains to a method of obtaining an individualized profileconcerning the amount of Gz load and duration likely to effect alowering of head blood flow of an individual to cause GLOC, the methodcomprising subjecting the individual to a Gz load increase gradient 900,monitoring the blood flow to the head through use of a pulse oximeter ata central location 910; determining the decrease of blood flow andduration of decrease blood flow that causes GLOC for the individual 920;obtaining a data profile for the individual 930; and loading the dataprofile onto an aircraft computer 940. The implementation of apersonalized data profile increases the accuracy of predicting when anindividual will undergo GLOC, and can therefore be used to better avertGLOC for the individual. In particular, the processing module containingthe data profile can establish a pre-GLOC condition for the individualthat when triggered will actuate an alarm and/or direct the aircraftcomputer to take corrective maneuvers. The terms “pre-GLOC condition” or“condition(s)” represent an empirically determined blood flow andduration conditions preceding GLOC for an individual, and likely to leadto GLOC, but which are established at a predetermined time sufficientlyin advance of GLOC so as to allow a pilot to react to avoid GLOC. Use ofthe personalized profile also will avoid unnecessary false alarms forthe individual, which will give the pilot more control over theaircraft, as the physiological conditions sufficient to induce GLOC willvary from pilot to pilot. The pilot can be subjected to Gz loads throughuse of a centrifuge, air flight maneuvers, or other Gz load producingmeans. The centrifuge is the most preferred means, as it can be closelycontrolled and monitored.

In an alternative embodiment, GLOC avoidance training can be implementedusing the methods of the subject invention. By closely monitoring thephysiological conditions leading up to GLOC for the individual pilot,each pilot can be trained to sense when they are about to enter GLOC andproperly react with the valsalva maneuver or other corrective actions.In a preferred embodiment, as part of the training process, the pilot isgiven a feedback signal to inform the pilot when he is entering apre-GLOC condition. This will assist in the pilot correlating internalfeelings and sensations associated with the pre-GLOC condition in orderto more quickly recognize the condition. Furthermore, as is discussed,infra, holding the valsalva maneuver too long can have acounter-productive effect. Utilizing the subject training methods willallow the pilot to practice and refine the optimal valsalva maneuvertechniques. Feedback signals may be implemented which will assist thepilot in properly timing the valsalva maneuver techniques.

Referring back to FIG. 5, in the system embodiment 50, the analyzer unit58 is shown as integrated into the aircraft computer 51. The aircraftcomputer 51 comprises a processing module 59 configured to automaticallyconduct a corrective flight maneuver with and/or without input from thepilot. The aircraft computer 51 is also connected to an alarm 55 that isactuated upon analyzer unit 58 sending a signal to said aircraftcomputer 51 indicating a predetermined low-level blood flow. In aspecific embodiment the detection and monitoring of changes in bloodflow comprises establishing a baseline value of plethysmography signalsunder normal Gz conditions, and then comparing later obtainedplethysmography signals to said baseline value. In a typical embodiment,the analyzer unit comprises a processing module configured to establishthe baseline value, continuously monitor the signals and compare to thebaseline value.

FIG. 6 shows an alternative embodiment system 60 for processing signalsobtained from a pulse oximeter probe being worn by a pilot andconducting a reaction responsive to certain information received fromsaid pulse oximeter probe. The system 60 comprises an analyzer unit 68is a stand-alone unit connected to wires 52 and 54. The analyzer unit 68is connected to an aircraft computer 61 through line 63 and directly toan alarm 65 through line 67. Upon the analyzer unit 68 determining lowblood flow, the analyzer unit 68 may actuate an alarm 65 in conjunctionwith sending the low blood volume signal the aircraft computer 61. Forthe sake of redundancy, the aircraft computer 61 may also connected tothe alarm 65 via wire 69. Like system embodiment 50, the aircraftcomputer 61 comprises at least one processing module (not shown)configured to conduct a corrective flight maneuver. It is alsocontemplated that such a system may also be used for the identifyingreduced blood flow to the head in patients and provide appropriatealarms. It may also serve as input into a control system. The controlsystem could adjust positive end expiratory pressure (PEEP), CPAP, orother ventilatory mode to ensure adequate blood flow, adjust oxygendelivery to ensure adequate central oxygenation, adjust drug or fluiddelivery systems, or automatically adjust certain controllable aspectsof the environment that may help alleviate decreased blood flow (e.g.decrease aircraft turn rate to decrease induced gravitational forces).See PCT application PCT/US06/15763.

The alarm 55 or 65 may be visual and/or audible in nature, such as alight being actuated on the flight panel or a speaker sounding an alarmsuch as a buzzer. The aircraft computer may also comprise at least oneprocessing module for directing the plane to take corrective flightmaneuvers designed to unload the wings of the aircraft so as to decreasethe Gz loads on the pilot. One example of such a maneuver includes, butis not limited to, leveling the plane to a steady attitude and altitudedecreasing the pitch to level flight attitude. Another example includesimmediately leveling the wings while in a steep (60-90 degrees bankangle) high speed turn. The wings' level attitude is designed to induceblood flow to the brain.

The term “aircraft” as used herein refers to any type of craft designedfor traveling above the ground. Aircraft is also used in a broader anduncommon sense as to refer to any traveling vehicle that, by the natureof its speed, acceleration and maneuvering, generates force that mayinduce GLOC in the operator of such aircraft, including vehiclesdesigned for operation on the ground.

The term “wire(s)” as used herein refers to any structure havingconductive properties to carry electrical signals. The term wire also isused in an uncommon fashion to denote that the two structures the termwire is used to connect may be substituted by a wireless means oftransmitting electrical signals between the two structures.Alternatively, where wires are used to carry signals from the probes toanother component, such wires may be substituted with a wireless meansof transferring the signals. For example, conventionaltransmitter/receiver devices could be implemented in the probe and thecomponent to which the probe sends it signals.

The term “communicatingly connected” as used herein refers to anyconnection either via wires or wireless connection, that is sufficientto convey electrical signals to and/or from at least two components thatare communicatingly connected.

As used herein, the terms “signals indicative of blood flow” refers tosignals corresponding to blood volume changes in tissue caused bypassage of blood, i.e., signals indicative of perfusion or blood flow.See Murray and Foster, The Peripheral Pulse Wave: InformationOverlooked, Journal of Clinical Monitoring, 12:365-377 (1996).Typically, these signals are derived from a pulse oximeter probe whichproduces a waveform produced as a result of absorption of deliveredenergy (e.g. via a light source) by hemoglobin in red blood cells. Suchsignals are referred to herein as plethysmography signals.

The term “processing module” may include a single processing device or aplurality of processing devices. Such a processing device may be amicroprocessor, micro-controller, digital signal processor,microcomputer, central processing unit, field programmable gate array,programmable logic device, state machine, logic circuitry, analogcircuitry, digital circuitry, and/or any device that manipulates signals(analog and/or digital) based on operational instructions. Theprocessing module may have operationally coupled thereto, or integratedtherewith, a memory device. The memory device may be a single memorydevice or a plurality of memory devices. Such a memory device may be aread-only memory, random access memory, volatile memory, non-volatilememory, static memory, dynamic memory, flash memory, and/or any devicethat stores digital information.

Turning to FIG. 7, a pre-auricular reflectance probe 500 is shown. Thepre-auricular region is the region in front of the ear. This probe 500comprises a wiring harness 515 having at its distal end 511 a probe basestructure 510 and at its proximal end 512 a connector 520. Thepre-auricular reflectance probe embodiment 500 is designed to be securedaround the user's ear with the probe base structure 510 typicallysecured just in front of the tragus of the ear. The probe base structure510 may be flexible but is preferably rigid or substantially rigid, soas to not bend or deform during use of the probe 500. In a preferredembodiment, the wiring harness is made of a flex circuit such as, butnot limited to, those offered by Minco Products, Inc., 7300 CommerceLane, Minneapolis, Minn. 55432-3177 U.S.A. or NorthPoint Technologies,207 E. Park Ave., Mundelein, Ill. 60060. The connector 520 may be anysuitable connector so as to bring the wires of the wiring harness 515into electrical communication with a corresponding receptacle withanother wire connected to the analyzer unit, or directly onto areceptacle on the analyzer unit.

As shown in FIG. 8, the wiring harness 515 comprise wires 516 made of aconductive substance sufficiently insulated. Wires in the wiring harness515 are connected to the LED 514 and the photodetector 512 (e.g., aphotodiode) of the probe base structure 510. The wiring harness 515 maybe provided with an adhesive material 524 that assists with thesecurement of the probe embodiment in place around the ear and in frontof the tragus. Before securing the probe 500 in place, a peel-back layer525 is removed and the adhesive material 524 adheres the probe to theskin of the user.

The pre-auricular reflectance probe 500 is designed to obtainplethysmography readings and/or oxygen saturation measurements of thetemporal artery. The temporal artery is an ideal target since itdirectly branches off the carotid artery (which is the primary artery toone hemisphere of the brain). The LED 514 directs light to the temporalartery, and depending on the amount of blood flow, or oxygen saturation,the blood in the temporal artery will absorb a quantum of the emittedlight. Some of the light is reflected out from the temporal artery andsensed by the photo-detector 512. The amount of light reflected isdirectly correlated with the amount of blood and/or oxygen saturation ofthe blood present in the artery. The spacing between the LED 514 andphotodetector 512 is critical for obtaining accurate measurements. Thespace between the LED 514 and photo-detector 512 is typically in therange of about 5 mm to about 35 mm. Preferably, the space is in therange of about 10 mm to about 20 mm. The most preferred range is of thespace is about 12 mm to about 16 mm.

In an alternative embodiment, the subject invention is directed to aprobe embodiment similar to the pre-auricular reflectance probe, or justthe probe base structure with the at least one LED and photodetector,which is embedded into a pilot's helmet, such as in the padding of thehelmet. The probe is embedded into the pilot's helmet at a location suchthat the probe is positioned and stabilized at the pre-auricular region,upon placement of the helmet on the user's head. Accordingly, in atypical embodiment, the probe is embedded in the padding of a helmetthat covers or is proximate to the user's ear. Similarly, the probe maybe embedded into or otherwise associated with a fireman's helmet such asthat shown in FIGS. 4D and 4E.

FIGS. 9-12 show a nasal probe embodiment 800 configured for obtainingplethysmography readings and/or oxygen saturation readings from theuser's nasal alar region. The nasal probe embodiment 800 comprises abase portion 813 which runs along the longitudinal ridge of the nose. Atthe distal end 833 of the base portion 813 is a bridge portion 819. Thebridge portion 819 runs transversely across the nose and comprises aright flap portion 812 at one end and a left flap portion 817 at itsleft end. The right and left flap portions 812, 817, respectively, arepositioned above the right and left nares of the user. The left flap 817has attached thereto or integrated therewith at least one LED 810 orother light source. Extending down from the right and left flaps 812,817 are a right extension 823 and a left extension 824. Attached to orintegrated with the left extension 824 is a wing fold 820 that isconfigured to be inserted into the user's left nostril. The wing fold820 has at its distal end a photodiode 825 attached thereto orintegrated therewith. The wing fold 820 is designed to bend over and beinserted into the user's nostril such that the photodiode 825 ispositioned directly across from the LED 810 located on the exterior ofthe user's' nose. Extension 823 comprises wing fold 814 which isdesigned to be inserted into the user's right nostril. The positioningof wing fold 814 in the user's right nostril provides a counter force tothe wing fold 820 which would tend to pull the probe 800 towards theleft. Thus, the right flap 812, right extension 823, and right wing fold814 act together to assist in securing the nasal probe 800 in place. Asshown in FIG. 11, the nasal probe 800 is provided with an adhesivematerial 835 and a peel-back layer 830. Before use, the peel-back layer830 is removed and the adhesive 835 assists in securing the nasal probe800 to the skin of the user's nose. At the proximal end 834 of the base813, a connector 840 is provided. Wires 836 are provided in the nasalprobe embodiment and run from the LED 810 and photodiode 825 up toconnector 840. Furthermore, a flex circuit as described above may beattached to or integrated with the probe embodiment 800 so as to providethe necessary wiring to the LED 810 and photodiode 825.

Through use of the novel alar probe design described above, theinventors discovered an unexpectedly superior probe position on thelateral side of the nostril just behind the prominent part, which isreferred to as the fibro-areolar tissue. The inventors have surmisedthat this part of the lateral nostril is supplied by the lateral nasalbranch of the facial artery, but there are several branches (similar toKiesselbach's plexus found on the nasal septum). This position alsoincludes the branches of the anterior ethmoidal artery anastamoses(lateral nasal branches), which is a branch off the internal carotid.Accordingly, the fibro-areolar tissue site is an unexpectedly optimalsite for positioned a probe for use to prevent GLOC. Thus, in apreferred embodiment, the alar probe 800 is dimensioned so thatplacement onto the fibro-areolar region is optimized for the user. Otherembodiments are contemplated as well, including clips, hooks; andreflectance designs for either inside or outside nose. which could beinconspicuous and would be especially advantageous for ambulatory andlong term use

According to an additional embodiment, the subject invention pertains toa probe designed for obtaining readings from the post-auricular region.As shown in FIG. 17, the post-auricular region 1711 is the region behindthe ear. The posterior auricular artery is a small branch directly offthe external carotid. It runs posterior to the auricle and superficialto the mastoid process of the temporal bone. The proximity to theexternal carotid means that readings from the post-auricular region canprovide improved insight to carotid blood flow than a probe on theforehead. Additionally, since collateral flow is not likely at thislocation it gives a good indication of unilateral flow through thecarotid. The other immediate advantage is the superficial nature of theartery coupled with the relative thin layer of skin covering it. Theforegoing features, plus the fact that the solid temporal bone isdirectly below, make the post-auricular region an ideal site forreflectance monitoring.

Another distinct advantage of the reflectance monitoring at thepost-auricular region is the lack of venous blood to interfere withsaturation readings, as sometimes experienced with forehead models. Thethin layer of skin and strong pulsation from the artery allows forcorrect arterial saturations to be calculated. Other benefits includethe lack of hair and fewer sebaceous and sweat glands to interfere withreadings. Finally, the area behind the ear is easy to secure a probe toand it is normally out of the way of other devices. Thus, according toanother embodiment, the subject invention pertains to a post-auricularreflectance probe 1700 comprising an elongated body portion 1710. Theelongated body portion 1710 is curved to wrap around at least a portionof the user's ear. The elongated body portion 1710 comprises a distalend 1713 and a proximal end 1714. At the proximal end 1714, theelongated body has attached thereto or integrated therewith a probe basestructure 1715. The probe base structure 1715 comprises at least one LED1716 and at least one photodetector 1717. The at least one LED 1716 andat least one photodetector 1717 are connected to and in electricalcommunication with wires 1718. The wires 1718 may extend from the probebase structure 1715 and end in a connector 1719. The wires may be ofvaried length depending on the application. For example, the wires mayend at the proximal end 1721 of the probe base structure 1715, or mayrun for length out of the probe base structure 1715 and connect to theaircraft computer, or components thereof (e.g. signal processing unit,analyzer unit, etc.).

In an alternative embodiment, the subject invention is directed to aprobe embodiment similar to the post-auricular reflectance probe 1700,or just the probe base structure 1715 with the at least one LED andphotodetector, which is embedded into a pilot's helmet, such as in thepadding of the helmet. The probe is embedded into the pilot's helmet ata location such that the probe is positioned and stabilized at thepost-auricular region, upon placement of the helmet on the user's head.

According to an additional embodiment, as shown in FIG. 18, the subjectinvention pertains to an ear canal probe embodiment 1800 for obtainingplethysmography readings from the ear canal, and more specifically thetympanic artery. The probe 1800 is tapered to assist in placement in theear, but may alternatively not be tapered. The probe comprises an innerend 1810 which is inserted into the ear canal first, and an outer end1820. An LED is 1812 is provided on one side of the probe 1800 with aphotodetector 1814 provided on the opposite side. Those skilled in theart will appreciate that the spatial arrangement and placement of theLED 1812 and photodetector 1814 may optimized by routineexperimentation. Connected to the LED 1812 and photodetector 1814 arewires 1822 and 1824, respectively, which come together to form wire1816. Wire 1816 exits out the outer end 1820 via exit 1818. The probe1800 is similar to that described in U.S. Pat. No. 5,213,099, but isspecifically tailored and used to obtain plethysmography readings fromthe ear canal The '099 patent teaches use of an ear canal probe toobtain oxygen saturation and pulse readings, but does not contemplate orteach use of plethysmography to monitor blood flow and as a method todiminish the risk of GLOC. The inventors have found that plethysmographyreadings are particularly advantageous in accurately monitoring bloodflow (or perfusion), and more accurately and quickly determiningpre-GLOC conditions.

All of the probes described above can utilize wireless technology. Thewireless technology can be used for telemetry which allows for remotemonitoring of multiple patients/personnel, or also to create a cablelesssystem for improved patient comfort. Numerous wireless protocols andsystems have been developed for sensor networks including Zigbee,802.14.5, 802.11 WiFi networks, and point-to-point networks likewireless USB, etc. Many of these new technologies are enabling verysmall integrated circuits and low power that could be embedded into theprobes themselves. The probes would contain small rechargeable orreplaceable batteries that would power the probe electronics as well asthe transmission back to a base station or central station formonitoring. The processing required on the data could be done largely atthe front-end (probe) or at the back-end (station) or some combinationthereof. A tradeoff between computing power and transmission power wouldbe required at the front end to minimize probe size, weight, and powerconsumption. For instance, higher processing power at the front endwould allow for reduced bandwidth and communication power in the probe.In another embodiment, an ultra low-power sensor could be powered viacapacitive coupling or RF power, thus removing the requirement for abattery pack.

An alternative embodiment would include a small cable from the sensor toa processing subsystem with power and either wired or wirelesscommunication capability. For instance, this processing subsystem couldbe placed behind the ear similar to a hearing aid. It could also beattached in various “dead” spaces of the helmet or mask system orattached in a convenient location using the straps that support the maskor helmet.

EXAMPLE 1

A pulse oximeter probe was positioned on the right cheek and left cheekof an individual. FIG. 13 a shows the right and left plethysmographreadings of the individual. At a point in time, the right carotid arteryof the individual was depressed thereby stopping blood flow. FIG. 13 bshows the effects of pressing on one carotid artery while monitoringfrom both cheeks. The amplitude of the signal from the right cheek probedramatically decreases (see arrow). FIG. 13 c shows that the when thecarotid artery is released, the plethysmography signal from the rightcheek spikes (hyperemic response, see arrow) and then returns to normalamplitude. During GLOC, the same or greater decrease in the amplitude ofthe plethysmograph would be experienced from any probe monitoring fromthe head. It is believed that the amount of Gz load sufficient to reduceblood flow to the brain, and/or induce GLOC, varies. By knowing whatpercentage of pre +Gz blood flow leads to GLOC in any individual pilot apersonal profile for the pilot may be produced that optimizes the alarmfor that individual.

EXAMPLE 2

The inventors have developed a new processing of the plethysmographysignal such that important information may be extrapolated from thesignal. This novel processing reveals information not before realized tobe obtainable from a plethysmography signal stream. In the past, theplethysmography signal stream was typically obtained from a peripheralsite such as the finger, or other extremity. It is the inventors' beliefthat obtaining the plethysmograph from a central site lacks much of thebackground noise found in the plethysmograph from a peripheral site, andit is the obtention of this “less noisy” signal that eventually led tothe realization that information such as respiration rate and venousimpedance can be extrapolated.

The raw signal stream obtained from a pulse-oximeter probe is related tothe amount of light from the LED that hits the photodetector of thepulse-oximeter probe. The magnitude of the signal from the photodetectoris inversely proportional to the amount of absorption of the lightbetween the LED and the photodetector (greater absorption results inless light exciting the photodetector). The absorbed light is due tomultiple factors, including absorption due to tissue, absorption due tovenous blood, absorption due to arterial blood, and absorption due tothe pulsation of arterial blood with each heart beat. Typically, the rawsignal from the photodetector is processed (e.g. removal of artifactsand autogain of the signal) and also separated into two components. Thetwo components are intended to be the time varying signals that arerelated to the beat-to-beat variations caused by the pulsation and flowof blood in the arteries (typically called the AC component), and theslowly varying components that is related to the other physiologic andphysical properties of the signal, typically called the DC component(including non-pulsatile arterial blood, pulsatile and non-pulsatilevenous blood and tissue and bone). The AC signal has been typicallycalled the plethysmography and the DC component overlooked. This isexplained in further detail below.

Typically, photoplethysmography is conducted using one pulse oximeterprobe. The raw signal stream obtained from a pulse oximeter probe isrelated to the amount of light from the LED that hits the photodetectorof the pulse oximeter probe. The magnitude of the signal from thephotodetector is inversely proportional to the amount of absorption ofthe light between the LED and the photodetector (greater absorptionresults in less light exciting the photodetector). The absorbed light isdue to multiple factors, including absorption due to tissue, absorptiondue to venous blood, absorption due to arterial blood, and absorptiondue to the pulsation of arterial blood with each heart beat. Typically,the raw signal from the photodetector is processed (e.g. removal ofartifacts and autogain of the signal) in order to obtain an arterialoxygen saturation value and the plethysmograph is largely ignored.Significant confusion and overlap exists in the terminology used indescribing various aspects of pulse oximetry. On one hand, the terms ACcomponent and DC component are used to describe the anatomicalstructures responsible for the photoplethysmograph (AC componentpulsatile blood flow in arteries, arterioles and possibly capillaries)and the components responsible for attenuating the signal (DCcomponent—venous blood, tissue, bone, etc.) The terms are also used todescribe the phasic rapid pulsatile flow in the arteries and arteriolesas seen in the plethysmography (AC component) as contrasted with slower(DC) components of the plethysmograph.

As the AC component and DC component can have different meanings in theart depending on the context of the situation, for the sake of furtherclarity, the AC component will also be referred to herein as the“pulsatile arterial” component (PAC), and the DC component will also bereferred to herein as the “venous impedance” component (VIC). Thus, weuse the term AC component to describe a component of a processedplethysmographic signal that represents the pulsatile blood flow that ispresent in the vascular bed being monitored. The DC component, as usedherein, is a phasic slower frequency signal that represents the venousimpedance of blood in the vascular bed being monitored and is influencedby variations in intrathoracic pressure and venous blood volume. Thepulsatile arterial signal has been typically called the plethysmographand the VIC overlooked, although it is present in the signal and can beisolated as described later. A further distinction must be made betweenthe term “DC component” and the term “DC offset”. The popular usage ofthe term DC component has been described above. The term “DC offset”refers to the amount that the plethysmographic signal is shifted from abaseline that would be present if no light excited the photodiode. Theplethysmographic signal is small relative to the magnitude of the DCoffset, and “rides” on the DC offset signal. The DC offset varies withthe intensity of the ZEDS and the amount of light absorbed by thetissues. Thus, if the light path through tissue remains constant, the DCoffset increases with increasing LED power, and decreased with less LEDpower. Alternatively, the DC offset increases as the path of lightthrough the tissues decreases and decreases as the path of light throughthe tissues increases. Manufacturers usually have circuits built intothe pulse oximeter to keep the LED power in a range in which the DCoffset will be an adequate signal to discern the photoplethysmograph,but less than that which will oversaturate the photodiode.

According to one signal processing method embodiment of the subjectinvention, the effects of the individual heart beats in theplethysmograph are separated out from the other information, which isfundamentally a different goal than conventional processing, which isbasically to obtain an adequate arterial component and discarding thevenous impedance component. Standard practice is to implement a DCremoval technique that involves removing the venous impedance componentby a low pass filter. This technique, however, does not sufficientlyseparate all of the data from the two sources of information. Thesubject processing method obtains a higher fidelity signal, which iscritical when dealing with precise measurements of variables fordetermining, for example, respiratory events in a patient.

In a specific embodiment, the high fidelity pulsatile arterial componentand the venous impedance component of the plethysmography signal(previously ignored by those in the art) are achieved by unique signalprocessing, comprising:

-   -   1) discretely selecting the peaks and troughs of the signal        (improved noise/artifact rejection can be achieved by looking        for peaks and troughs that exist at the expected heart rate,        estimated by Fourier or autocorrelation analysis, or from past        good data)    -   2) finding the midpoints between peaks and troughs or extreme        values and interpolating between these values (possibly        including smoothing or splining this interpolated signal)    -   3) extracting the venous impedance component as the interpolated        and possibly smoothed line    -   4) extracting the pulsatile arterial component as the raw signal        subtracted from the venous impedance component.

This processing is preferably implemented from signals obtained from acentral source site, but it could be applied to signals obtained fromother sites so long as the fidelity of the signal is sufficiently highand reliable. This technique achieves a nonlinear filter with zero delayand optimally separates the two signals of interest. In view of theteachings herein, those skilled in the art will appreciate that similartechniques for achieving these objectives could also be adapted, and aredifferentiated from the conventional processing of plethysmographysignals due to their goal of optimally separating the two signals ofinterest on a beat-to-beat, zero delay basis (unlike standard linearfiltering, DC removal techniques, and averaging techniques).

The AC and DC components, as described herein, are intended to be thetime varying signals that are related to the beat-to-beat variationscaused by the pulsation and therefore, when recorded over time, the flowof blood in the arteries (the AC component, although different from theAC component described by others), and the slowly varying componentsthat are related to the other physiologic and physical properties of thesignal related to the impedance of the venous vessels and the changes inintrathoracic pressure, the venous (DC) component which differs from the“classical” description of the DC component which is said to includenon-pulsatile arterial blood, pulsatile and non-pulsatile venous bloodand tissue and bone. The amplitude and area under the curve (AUC) of theAC component contains information about the amount of arterial bloodflowing past the detector. In order to correctly interpret thisinformation, the AC and DC components must be separated more rigorouslythan with the algorithms in standard monitors and previously describedin the literature. In particular, the pulsatile arterial componentshould contain only that information that relates to beat-to-beatvariations of the heart. The DC component should contain lower frequencyeffects from physiology (such as the respiratory effects, blood pooling,venous impedance, etc.) and physical sensor changes (e.g. changes in theorientation of the probe, etc.).

Accordingly, the inventors have discovered and characterized for thefirst time at least three separate components of the plethysmographsignal: (a) blood pulsation signal, (b) time-varying DC signal or venousimpedance signal, and (c) the classical DC component signal which is afunction of the tissue (muscle, bone, etc) at the probe site, and is thebaseline DC component on which the venous impedance signal rides.

Pulse oximeter probes useful in accordance with the teachings hereininclude, but are not limited to, those described in co-pending U.S.application Ser. Nos. 10/176,310; 10/751,308; 10/749,471; and60/600,548, the disclosures of which are all incorporated herein intheir entirety.

As referred to above, the VIC of the photoplethysmograph is an indicatorof venous impedance, while the PAC is a measure of regional blood flow.During forced airway maneuvers, intrathoracic pressure changesdramatically. These pressure changes are transmitted directly to theveins in the head, because there are no anatomical valves in veinsleading to the head. Changes in intrathoracic pressure have directeffects on both the beat to beat pulsatile arterial blood flow (PAC),and the amount of venous blood in the vascular bed being monitored on abreath to breath basis. These effects are present even during quietbreathing, but are far more pronounced with “airway maneuvers” such asthe Valsalva and Mueller maneuvers, and during exacerbation ofrespiratory conditions which increase airway resistance and/or decreaselung compliance. These pronounced changes are often referred to as“pulsus paradoxus” when measured by arterial blood pressure or directarterial blood monitoring. All conditions which affect airway resistance(increase) and lung compliance (decreased) increase the respiratorymuscle work (work of breathing for each breath, or power of breathingfor the amount of work performed in one minute). As the work or power ofbreathing increases, there are wider swings in intrathoracic pressurewhich in turn lead to phasic variations in pulsatile arterial blood flowand venous impedance. Respiratory rate can be easily determined whenmonitoring at “central source sites” and the degree of change in boththe AC and DC components are related to the degree of airway obstructionand/or lung compliance. At a given level of resistance and orcompliance, variations in the amplitude and AUC of both components canalso be an indication of volume status. Thus, a plethora of informationon both respiratory and cardiopulmonary mechanics can be ascertainedfrom the processed plethysmograph, especially when it is obtained from a“central source site”.

Algorithms to evaluate the PAC and VIC include, but are not limited to,separating the high frequency information in the PAC (heart rate andabove, typically above 0.75 Hz) information, the low frequencyinformation in the VIC (e.g. respiratory rate and changes in blood flow,typically from 0.05 Hz to 0.75 Hz) and the very low frequencyinformation in the DC offset (e.g. changes in pulse oximeter path length(positioning), typically less than 0.05 Hz). Separating these waveformswithout delays or significant averaging is required to optimally extractinformation from the photoplethysmograph (PPG). The PPG typically hasonly 2-3 heart beats (the major feature of the signal) for each breath(the second largest signal). If significant averaging or delays exist,the secondary signal (VIC) cannot be reliably separated from the primarysignal (PAC). Other methods exist that can be utilized to extract thesesignals. Wavelets allow for finer resolution at low frequencies than themore standard Fourier spectral analysis methods. Adaptive filtering mayalso be used to optimally adjust the cutoff frequency between thebreathing rate and heart rate. If coarse information is all that isrequired, many standard methods can be used to separate the signals,including linear filtering, frequency domain filtering, time domainanalysis such as zero-crossings and moving averages, nonlinearfiltering, modeling such as kalman filtering and ARMA modeling, andother methods known to those skilled in the art.

Quantification of the PAC and VIC changes can include peak or troughcounting, peak-peak timing, peak-trough height, area under the curve,shape of the curves, frequency characteristics of the curves, entropy ofthe curves, changes in the positions of the peaks, troughs, or midpointsfrom heart beat to heart beat or breath to breath. Some of theseparameters may need to be normalized by the LED signal power, DC offset,or the physiology of the probe placement.

Further, noise reduction techniques can be derived that will providemore robust detection of blood flow as well as standard pulse-oximetrytechniques. Signal processing techniques such as blind sourceseparation, adaptive noise cancellation, or other techniques that canisolate signals from difference sources can be applied to produce usablesignals in the presence of large artifacts. Two different approaches canbe applied. First, is to detect similarities in the artifacts for eachchannel and subtract the similar artifact (or prediction of the artifactfrom one sensor output to the other) from the raw sensor outputs. Thiswould leave a cleaner signal with less motion artifacts. This approachwill be preferred when the artifacts in multiple sensors are highlycorrelated, like when the sensors are attached to a single rigidstructure and motion in one causes motion in the other.

The second approach assumes that the noise/artifacts are different butthe underlying desired signal is similar. In this case, the algorithmswould search for the common characteristics in each sensor output andremove signals that are highly variable between the channels. Thisapproach could be very successful if the sensors are not collocated onthe same rigid structure (e.g. you have independent noise sources) or ifthe noise/artifacts are highly dependent on the exact path that thelight travels.

The above listed methods do not require that the signals come fromsimilar sensors. For instance, auxiliary sensors can be used todetermine motion artifacts are present and assist in the removal of suchartifacts. One approach is to use one or more accelerometers that candetect rapid positional changes of the probe and correlate these changeswith the PPG signals. Other sensors that detect or suffer from similarmotion artifacts can also be used.

In another embodiment, an approach with multiple LEDs/photodiodes couldbe implemented where multiple LED/photodiode pairs are utilized andfrequent testing of the signal quality produced by each pair is used.The highest quality signal could then be used and this selection couldbe changed over time. This would allow for more easily producing goodquality signals without requiring accurate placement or ensuring thatthe sensors do not move over time. As described above, it is alsopossible to use multiple sensors simultaneously for improved dataquality and these sensors could be selected from the set of availablepairs. For example, multiple pairs of reflectance probes could be placedon the structure of FIG. 8, including multiple locations in thepre-auricular and post-auricular area. This would allow for physiologicvariability from subject to subject and motion and non-optimal fit ofthe appliance to the subject.

FIG. 14 represents a plethysmograph from a pulse oximeter probepositioned on the cheek. The AC component is provided on the top and theDC component is provided on the bottom. Pressing on the carotiddiminishes blood flow, as seen in the AC component (see arrow).Conversely, the DC component goes up when the carotid is depressed (seearrows). This confirms the inventors' beliefs of the physiologicalphenomenon that is represented in the DC component. That is, for thisexample, the DC component increasing demonstrates that there is bothless blood flowing to the cheek, and because only the artery in occludedbut not venous return there is low venous impedance. The effect is thatless blood is flowing to the check, but that blood is able to leave thecheck. Since there is less blood between the LED and photodetector,there is less absorption of the signal, resulting in a higher DCcomponent signal.

By separating the AC and DC components the effects on arterial bloodflow and venous return can both be evaluated, a desirable feature whenmonitoring variables for GLOC.

EXAMPLE 3

In FIG. 15, the DC component is plotted at the top and the AC componentat the bottom. A finger probe was initially placed at heart level and a“baseline” AC component amplitude was obtained. The individual performeda Valsalva maneuver similar to what pilots are taught to do duringsustained +Gz in order to prevent GLOC. However, the Valsalva was heldfor over 10 seconds and this resulted in a decrease in blood flow(reduction in AC component amplitude), a common problem causing GLOC(holding the positive pressure for too long).

Next, the individual placed his finger above the level of his head(while standing up). This results in the amplitude of the AC componentincreasing. This contradicts convention teaching regarding the ACcomponent, which would predict the exact opposite result anddemonstrates the effects of local vessel reactivity to a change inposition relative to the heart. The AC component increases because thereis LESS venous impedance and more blood flow probably due to localvasodilatation in arterioles in the finger between the LED and thedetector and there is less venous blood in the finger as demonstrated bythe increase in the DC component. The individual again performed aValsalva maneuver and the blood flow (AC component) decreased and didthe DC component due to diminished venous return.

Finally, the individual held his hand below the level of his heart. Asthe present new understanding of the different components ofplethysmography signals would predict, the AC component decreasedbecause of increased venous impedance and a decreased pressure gradientbetween the arterioles and the venules and the DC component decreasedbecause there was more blood pooled on the venous side between the LEDand the photodetector. The same result as above occurred during theValsalva maneuver. Also note that there is a small, but detectable,decrease in the DC component with each Valsalva. The foregoing furtherdemonstrates that the DC component must be adequately separated in orderto obtain a highly accurate AC component signal and to demonstrateeffects of the venous side (i.e. venous return).

The subject invention can serve as an early warning system in theclinical environment and provide the clinican with a warning that theblood flow is decreasing and can also be integrated into closed loopsystem. The control system could adjust positive end expiratory pressure(PEEP), CPAP, or other ventilatory mode to ensure adequate blood flow,adjust oxygen delivery to ensure adequate central oxygenation, adjustdrug and fluid delivery systems, or automatically adjust certaincontrollable aspects of the environment that may help alleviatedecreased blood flow (e.g. decrease aircraft turn rate to decreaseinduced gravitational forces).

While various embodiments of the present invention have been shown anddescribed herein, it will be obvious that such embodiments are providedby way of example only. Numerous variations, changes and substitutionsmay be made without departing from the invention herein. Accordingly, itis intended that the invention be limited only by the spirit and scopeof the appended claims. The teachings of all patents and otherreferences cited herein are incorporated herein by reference to theextent they are not inconsistent with the teachings herein.

The invention claimed is:
 1. A method of monitoring blood flow status tothe head of an individual, said method comprising: securing a pulseoximeter probe to a central source site of said individual andgenerating a plethysmography waveform; extracting an isolated DCcomponent waveform from said plethysmography waveform with a signalprocessor; monitoring blood flow at said central source site bycontinuously monitoring changes in said isolated DC component waveformover time; and effecting a predetermined reaction responsive to saidblood flow falling below a predefined value.
 2. The method of claim 1wherein said reaction comprises generating an alarm.
 3. The method ofclaim 2 wherein said alarm is a visual, tactile or audible warning. 4.The method of claim l wherein said reaction comprises directing flightcontrol systems of an aircraft to undertake a corrective flightmaneuver.
 5. The method of claim 1, Wherein said monitoring blood flowcomprises establishing a baseline value of plethysmography signals andcomparing subsequently Obtained plethysmography signals to said baselinevalue.
 6. The method of claim 1, further comprising sustaining andmonitoring said isolated AC component waveform.
 7. A system formonitoring blood flow status of a subject comprising a pulse oximeterprobe that secures to a central source site of said subject andgenerates a plethysmography waveform; a signal processor incommunication with said pulse oximeter probe, wherein said signalprocessor extracts an isolated DC component waveform from saidplethysmography waveform and sustains said isolated DC componentwaveform and, optionally, an isolated AC component waveform; and ananalyzer unit in communication with said signal processor, wherein saidanalyzer unit monitors blood flow by continuously evaluating changes insaid isolated DC component waveform and, optionally, said isolated ACcomponent waveform, over time.
 8. A system for monitoring blood flowcomprising a mask that delivers gas to a subject, said mask comprising acompartment that covers the nose and/or mouth of said subject and anairhose attached to said compartment; and a pulse oximeter probe thatsecures to a central source site of said subject and generates aplethysmography waveform, said pulse oximeter probe associated with saidmask, a signal processor in communication with said pulse oximeter probethat extracts an isolated DC component waveform from saidplethysmography waveform and sustains said isolated DC componentwaveform and, optionally, an isolated AC component waveform; and ananalyzer unit in communication with said signal processor, wherein saidanalyzer unit monitors blood flow by continuously evaluating changes insaid isolated DC component waveform and, optionally, said isolated ACcomponent waveform, over time.
 9. The system of claim 8, wherein saidpulse oximeter probe secured to said subject's nasal alar and comprises:an elongated base positioned along said subject's nasal ridge, saidelongated base comprising a proximal end and a distal end; a bridgeattached to or integral with said proximal end of said elongated base,said bridge having a right end portion and a left end portion; a rightflap extending from said right end portion of said bridge; a left flapextending from said left end portion of said bridge; at least one LEDdisposed in either said right flap or said left flap, or both; and atleast one wing fold extending down from either said right flap or saidleft flap, or both, said at least one wing fold comprising at least onephotodetector disposed thereon and inserted into said user's right orleft nostril such that said at least one photodetector is aligned acrossfrom said at least one LED.
 10. The system of claim 9, wherein saidpulse oximeter probe comprises a first wing fold extending down fromeither said right flap or said left flap, said first wing foldcomprising at least one photodetector disposed thereon and inserted intosaid subject's right or left nostril; and a second wing fold extendingdown from either said right flap or said left flap, whichever said firstflap is not extending down from, and inserted into said user's right orleft nostril, wherein said first wing fold and said second wing fold aresufficiently rigid so as to hold their shape upon insertion into saiduser's nostrils.
 11. The system of claim 8, further comprising aconnector attached to or integrated at the proximal end of saidelongated base, said connecter attached and in electrical communicationwith a corresponding receptacle.
 12. The system of claim 8, where saidmask further comprises a strap that holds said mask to said subject'sface and wherein said pulse oximeter probe is a reflectance probeassociated with said strap, said reflectance probe located along saidstrap so as to facilitate obtaining readings from said subject'spre-auricular region or post-auricular region.
 13. The system of claim12, wherein said reflectance probe comprises a probe base structureattached to or integrated with said strap; at least one LED disposed onsaid probe base structure; and at least one photodetector disposed onsaid probe base structure and spaced proximally up from said at leastone LED disposed on said probe base structure.
 14. The system of claim13, further comprising a connector attached to or integrated with aproximal end of a wiring harness.
 15. The system of claim 13, whereinsaid at least one LED is positioned distal to said at least onephotodetector at a spacing in the range of about 5 mm to about 30 mm.16. The system of claim 13, wherein said at least one LED is positioneddistal to said at least one photodetector at a spacing in the range ofabout 8 min to about 20 mm.
 17. The system of claim 13, wherein said atleast one LED is positioned distal to said photodetector at a spacing inthe range of about 10 mm to about 12 mm.
 18. The system of claim 8,wherein said probe is communicatingly connected to a wirelesstransmitter.
 19. The system of claim 8, wherein said probe comprises abattery.
 20. A system for monitoring signals indicative of blood flow atleast one central source site of at least one subject, said systemcomprising a mask that delivers gas to said subject; at least one pulseoximeter probe that secures to a central source site of said subject andgenerates a plethysmography waveform; and a remote monitoring computercommunicatingly connected with said at least one pulse oximeter probe,wherein said remote monitoring computer processes said plethysmographywaveform, wherein said remote monitoring computer extracts an isolatedDC component waveform, and monitors blood flow by continuouslyevaluating changes in said isolated DC component waveform over time. 21.The system of claim 20, wherein said at least one subject is anemergency responder and said at least one puke oximeter probe comprisesa wireless transmitter.
 22. The system of claim 20, wherein said atleast one subject is a patient in a medical facility.
 23. The system ofclaim 20, wherein said remote monitoring computer determines determineoxygen saturation.
 24. The system of claim 20, wherein said mask furthercomprises a capnography sensor associated therewith, said capnographysensor being communicatingly connected to said remote monitoringcomputer.
 25. The system of claim 20, wherein said mask furthercomprises a sampling apparatus to obtain exhaled gases for determinationof carbon dioxide content within said mask and communicatingly connectedto a capnography analyzer.
 26. The system of claim 25, wherein saidremote monitoring computer is communicatingly connected to saidcapnography analyzer and configured to process signals from saidcapnography analyzer.
 27. A mask for delivering gas to a subject, saidmask comprising a nasal delivery portion; at least one projectionassociated with said nasal delivery portion that inserts into at leastone nasal passage; an airhose associated with said nasal deliveryportion; and a pulse oximeter probe that secures to a central sourcesite of said subject, said pulse oximeter probe associated with saidmask, a signal processor in communication with said pulse oximeter probethat extracts an isolated DC component waveform from saidplethysmography waveform and sustains said isolated DC componentwaveform and, optionally, an isolated AC component waveform; and ananalyzer unit in communication with said signal processing unit, whereinsaid analyzer unit monitors blood flow by continuously evaluatingchanges in said isolated DC component waveform and, optionally, said ACcomponent waveform, over time.
 28. The system of claim 27, furthercomprising a strap that holds said mask to said subject's face andwherein the pulse oximeter probe is a reflectance probe associated withsaid strap, said reflectance probe located along said strap so as tofacilitate obtaining readings from said subject's pre-auricular regionor post-auricular region.
 29. The system of claim 27, wherein said maskfurther comprises a wire connected to said probe, a battery connected tosaid wire and a wireless transmitter communicatingly connected to saidprobe.